The United States entered the war to stop the spread of Communism in Southeast Asia. American leaders feared that Communist forces would gain control of Vietnam. They believed in the domino-theory which meant that if Vietnam fell into communism, it would drag other countries in Asia to communism. Vietnam had been split in half in 1954 after a long war of independence against the French since 1946. When the French were defeated in the battle of Diem Bien Phu they withdrew from Vietnam. After the peace resolution in Geneva the country was split in half. The north became communist under the leadership of Ho Chi Min whilst the south became anti-Communist under the leadership of Dinh Diem. The government from the south was weak, ineffective and unpopular. However the USA supported it since Diem was anticommunist. The north wanted to unite Vietnam under a communist nation; however Americans were determined to prevent this.
The gulf of Tonkin incident. An American destroyer, the USS Maddox was attacked by North Vietnamese torpedo boats while it was making some intelligence reconnaissance missions in the gulf of Tonkin. Americans took this as a serious act of war. North Vietnamese actions violated the UN charter, which enable president Johnson to pass this event to congress. Johnson wanted to intervene militarily in Vietnam but needed the approval of the congress. The congress approved, through the Gulf of Tonkin resolution that a conventional use of military force in South East Asia was needed. They basically gave Johnson a “blank cheque” to do what he wanted in Vietnam.
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